Find all available clang libs.  Fixes issue with linking Canal to Clang 3.1 on Fedora 18.
initial work on string tries
created a StringTrie domain with default constructor and domain operation definitions
added StringTrie tests for setTop and setBottom operations
added string trie constructors inspired by StringPrefix class
small string trie test fix
Merge branch 'string_trie' of github.com:karelklic/canal into string_trie

Conflicts:
	tests/ArrayStringTrieTest.cpp